Method of absorbing thermal energy at low temperatures and apparatus for carrying out such methods



N 1955 J. R. VAN GEUNS ETAL 3,

METHOD OF ABSCBBING THERMAL ENERGY AT LOW TEMPERATURES AND APPARATUS FOR CARRYING OUT SUCH METHODS Filed July 16, 1963 2 Sheets-Sheet 1 21 11 24 i H; 7 j l in- 3 5 INVENTORS ZiMA/K AGENT 1965 J. R. VAN GEUNS ETAL 3,214,924

METHOD OF ABSORBING THERMAL ENERGY AT LOW TEMPERATURES AND APPARATUS FOR CARRYING OUT SUCH METHODS Flled July 16, 1963 2 Sheets-Sheet 2 F I 4 INVENTORS JOHANNES R.VAN ceuus GIJSBERT PR I AST BY v

GENT United States Patent 3,214,924 METHOD OF ABSQRBING THERMAL ENERGY AT LOW TEMPERATURES AND APPARATUS FGR CARRYING OUT SUCH MTETHODS Johannes Rndolphus van Genus and Gijshert Prast, Emmasingel, Eindhoven, Netherlands, assiguors to North American Philips Company, Inc, New York, N .Y., a corporation of Delaware Filed July 16, 1963, Ser. No. 295,414 Claims priority, application Netherlands, July 26, 1962, 281,45? 2 Ciairns. (c1. 62-6) The invention relates to a method of absorbing thermal energy at low temperatures, in which a working medium is alternately compressed, when it is substantially contained in one or more spaces having a higher mean temperature, and expanded, when it is substantially contained in one or more spaces having a lower mean temperature, while it is passed through a heat exchange, for example a regenerator, on its way from one space to the other, so as to deliver thermal energy when flowing to the expansion space and to absorb thermal energy when flowing from the expansion space.

A great variety of apparatus are known in which thermal energy is absorbed in the above described manner by expansion of a gas. Examples of such apparatus are cold gas refrigerators, expansion turbines and expansion reciprocating apparatus.

Such apparatus has a limitation in that, as is generally stated (see for example Handbuch der Kaltetechnik by Dr. Ing. H. Hausen, 1957, page 186, last five lines), it no longer operates satisfactorily when the temperature of the workibng medium falls to a temperature such that liquid is formed during the expansion. This means that the use of a given working medium prevents temperatures from being reached which are lower than the critical temperature of said working medium. In other words, in an apparatus of this kind employing a given working medium the same working medium cannot be liquefied in practice.

It is an object of the present invention to absorb thermal energy wth the aid of a given working medium at temperatures below the critical temperature of this medium.

The invention is based on the recognition of the fact that when the working medium is maintained above its critical pressure, no change of state occurs when cooling the medium below its critical temperature, so that no liquid is formed.

The method in accordance with the invention is characterized in that the pressure of the working medium is continuously maintained higher than a pressure which is at least substantially equal to the critical pressure of this medium, and in that the temperature at which the expansion takes place lies below the critical temperature of the medium in at least one of the spaces in which expansion takes place.

By this method there has occurred the surprising result in which thermal energy has been absorbed with the aid of a cold gas refrigerator employing hydrogen as the working medium at temperatures below the critical temperature of hydrogen. This enables hydrogen to be liquefied at the cold end of the refrigerator. Due to the slight compressibility of gas at its critical pressure and temperature a compression ratio was reached which is very high for apparatus of this kind.

Moreover, due to the slight compressibility of a gas above its critical pressure normal expansion is hardly feasible without the pressure falling below the critical pressure. Therefore in the present application the term expansion is to be understood to mean a reduction of 3,2l4,92 i Patented Nov. 2, 1965 the pressure of the working medium while withdrawing mechanical energy, this reduced pressure still exceeding the critical pressure of the medium.

A further embodiment of the method in accordance with the invention is characterized in that the medium is periodically compressed to above its critical pressure and then is supplied, while this pressure is maintained substantially constant, through a heat exchanger in which the medium delivers thermal energy and is cooled below its critical temperature, to an expansion space, after which while Withdrawing mechanical energy the pressure of the medium is decreased to a pressure which still exceeds the critical pressure, and consequently, the medium, while its pressure is maintained substantially constant, is discharged from the expansion space through a heat exchanger in which it absorbs thermal energy.

The invention further relates to an apparatus for the absorption of thermal energy at low temperatures, said apparatus comprising one or more compression spaces which in operation have a higher mean temperature and one or more expansion spaces which in operation have a lower mean temperature, the connection between the said two spaces including a heat exchanger through which a working medium can flow from one space to the other and vice versa, provision being further made of a drivingmechanism for driving the apparatus. According to the invention the said apparatus is characterized in that the driving mechanism and the walls of the compression and expansion spaces and of the heat exchanger are designed so that the apparatus is suited to operation at pressures higher than the critical pressure of the medium.

A further favourable embodiment of the apparatus in accordance with the invention, which is in the form of a cold gas refrigerator and is provided with at least one compression space of variable volume and at least one expansion space of variable volume which is in open communication with the compression space, these spaces having mutually dillerent mean temperatures in the operation of the apparatus, while the connection between the spaces includes heat exchangers, preferably regenerators, through which a medium can flow from one space to the other and vice versa, is characterized in that the working space contains a medium at a pressure which continuously exceeds a pressure which is at least substantially equal to the critical pressure of this medium, the temperature prevailing in at least one of the expansion spaces being below the critical temperature of the Working medium.

A further favourable embodiment of an apparatus in accordance with the invention for the absorption of thermal energy at temperatures below 30 K. is characterized in that the working medium contained in the working space is hydrogen.

A further favourable embodiment of an apparatus in accordance with the invention for the absorption of thermal energy at temperatures below 5 K. is characterized in that the working medium contained in the working space is helium.

Thus in the above mentioned apparatus thermal energy is absorbed at temperatures below the critical temperature of the working medium.

The invention will now be described in greater detail with reference to the drawings, in which:

FIG. 1 is a diagrammatic sectional view of a cold gas refrigerator of the displacer type constructed in accordance with the teachings of the present invention.

FIG. 2 is a diagrammatic sectional view of the apparatus for absorption of thermal energy in accordance with the teachings of the present invention and incorporating a double-acting piston.

FIG. 3 is a diagrammatic sectional view of another embodiment of the invention.

FIG. 4 is a sectional view of the three-space refrigerator utilized in another form of the present invention and FIG. is a diagrammatic sectional view of another embodiment of invention incorporating the absorption of thermal energy at low temperatures.

FIGURE 1 shows a cold gas refrigerator of the displacer type. In this cold gas refrigerator a displacer 1 and a piston 2 are connected by a displacer rod 3 and a piston rod 4 respectively to the cross-heads 5 and 6 of a rhombic drive 7. The displacer 1 is capable of movement in a cylinder 8 while the piston 2 is capable of movement in a cylinder 9. The cylinder 8 is surrounded by an annular channel including a cooler 10, a regenerator 11 and a freezer 12.

The apparatus operates as follows. A gas above its critical pressure is made to fill the working spaces which comprise a compression space 13, an expansion space 14 and the spaces in the cooler, regenerator and freezer. When the piston 2 is raised the gas, which at this instant is substantially contained in the compression space 13, is compressed. By the subsequent downward movement of the displacer 1 the gas in the compression space 13 is displaced to the expansion space 14 and in its flow delivers thermal energy in the regenerator 11 and is cooled to a temperature below the critical temperature. In the next stage the pressure of the gas, which now is substantially contained in the expansion space, is slightly decreased by a small downward movement of the piston 2 and subsequently the gas in expelled from the expansion space by the upward movement of the displacer 1. The gas flowing from the expansion space 14 to the compression space 13 passes through the regenerator 11, where it absorbs thermal energy. It will be appreciated that in filling the expansion space 14 the gas performs more work than is supplied to it by the displacer when it is expelled from the expansion space. Thus the upper surface of the displacer 1 withdraws work so that thermal energy is absorbed.

FIGURE 2 shows an embodiment of an apparatus for the absorption of thermal energy which comprises a piston 21 adapted to reciprocate in a cylinder 22. The piston 21 is rigidly connected to a piston 23 adapted to reciprocate in a cylinder 24. The pistons 21 and 23 are connected by a piston rod 25 to a driving device (not shown). The apparatus further includes a regenerator 26 and a supply container 27. It is also provided with two check valves 28 and 29 and two controlled valves 30 and 31.

This apparatus operates as follows. The spaces in the apparatus are filled with a gas above its critical pressure. When both pistons 21 and 23 are at outer dead centre, the valve 30 is opened and the gas flows from the supply container 27 through the regenerator 26, in which it is cooled below its critical temperature, to the expansion chamber 32. The pistons 21 and 23 then move downward. When the pistons 21 and 23 have travelled the greater part of their downstroke, the valve 30 is closed and the pressure of the gas contained in the expansion space 32 is decreased on further downward movement of the piston 21. In the subsequent upstroke of the piston 21, the gas is expelled from the space 32 while the valve 31 is opened so that the gas can flow through the regenerator 26 and a duct 33 to a compression space 34, in which it is compressed by the downstroke of the piston 23 and returned to the supply container 27. In this apparatus also the upper surface of the piston 21 extracts mechanical energy from the gas so that thermal energy is absorbed in the expansion space 32.

FIGURE 3 shows another apparatus in which the method in accordance with the invention can be carried out. This apparatus has a piston 41 adapted to reciprocate in a cylinder 42. The piston 41 is connected by a connecting rod 43 to a crank 44 which can be driven by a driving mechanism (not shown). A space 40 above the piston 41 is connected to a regenerator 46 by a pipe 45. A gas supply pipe 47 including a controllable valve 48 is connected at one end to the other side of the regenerator and at its other end to a supply container 49. To said other side of the regenerator 46 is also connected a gas discharge pipe 50 which includes a controllable valve 51 and the other end of which is connected to a supply container 52. The supply container 52 is connected to the supply container 49 through a pipe 53 including a compressor 54.

This apparatus operates as follows. When the piston 41 is in its uppermost position, the valve 43 is opened and gas above its critical pressure flows from the supply container 49 through the pipe 47, the regenerator 46 and the pipe 45 into the space 40. In the regenerator 46 the gas is cooled below its critical temperature. When the piston 41 has at least substantially reached its lowermost position, the valve 43 is closed and the valve 51 is opened. As a result the pressure of the gas in the space 40 decreases to the pressure which prevails in the supply container 52 but still is above the critical pressure. The gas is then expelled from the space 40 by the piston 41 and again passes through the regenerator 46 in which absorbs thermal energy. It will be appreciated that the gas flowing into the space 40 delivers more energy to the piston 41 than is supplied to the gas by this piston 41 during the expulsion of the gas from the space 40. Thus thermal energy is again absorbed.

FIGURE 4 shows an embodiment of a so-called threespace cold gas refrigerator. This refrigerator has a compression piston 61 which by connecting rods 62 is connected to a crank shaft 63 which is provided with a flywheel 64 and can be driven by a driving mechanism (not shown). The compression piston 61 can reciprocate in a cylinder 65. The apparatus further comprises a displacer 66 which is connected to the crank shaft 63 by a displacer rod 67 guided by the compression piston 61 and a connecting rod 68.

The displacer 66 comprises a portion 69 of greater diameter and a portion 70 of smaller diameter.

The portion 69 can reciprocate in a cylinder 71 which is surrounded by a cooler 72, a regenerator 73 and a freezer 74.

The portion 70 can reciprocate in a cylinder 75 which is surrounded by a regenerator 76 and a freezer 77.

This apparatus operates as follows. The working space is filled with a working medium above its critical pressure. The crankshaft 63 is then driven. Starting from the situation in which the compression piston 61 is substantially in its lowermost position and the displacer 66 in its uppermost position, the followng cycle takes place. The compression piston 61 moves up so that the working medium, which at this instant is mainly contained in a compression space 78, is compressed. The displacer 66 then moves down so that the medium is conveyed from the compression space 78 to an expansion space 79 and an intermediate space 80. In this transport the medium is cooled in the regenerators 73 and 76. At least in the regenerator 76 it is cooled to an extent such that the medium enters the expansion space 79 at a temperature below the critical temperature of this medium. The compression piston 61 then moves slightly downward so that the pressure of the working medium, which at this instant is mainly contained in the expansion space 79 and the intermediate space 80, is reduced. The displacer 66 is then moved upward so that the medium is expelled from the expansion space 79 by the upper face 81 of the displacer and from the intermediate space 80 by the annular surface 82 constituted by the junction of the portions 69 and 7!). It will be appreciated that in this expulsion the surfaces 81 and 82 deliver less energy to the medium than the gas has delivered to the displacer in filling these spaces. Hence thermal energy will be absorbed.

With the aid of the above described apparatus thermal energy has been absorbed at temperatures lower than the critical temperature of the working medium. The working medium used was hydrogen.

FIGURE 5 shows another embodiment of an apparatus for the absorption of thermal energy at low temperatures.

This apparatus comprises a compressor 91, a first heat exchanger 92, an expansion cylinder 93 containing an expansion piston 94, and a second heat exchanger 95.

This apparatus operates as follows. The working medium is compressed above its critical temperature by the compressor 91. This working medium then flows through the heat exchanger 92, in which it is cooled below its critical temperature in counterfiow with expanded medium to the expansion cylinder 93. In this cylinder the pressure of the medium is reduced while Withdrawing mechanical energy. This reduced pressure, however, still exceeds the critical pressure. The medium is then expelled from the expansion cylinder 93 by the piston 94. It will be appreciated that thermal energy is again absorbed in the expansion cylinder. The expelled medium then flows to the heat exchanger 95, in which it exchanges heat with a medium to be cooled which is contained in a pipe 96. After absorbing thermal energy the medium flows back through the heat exchanger 92 to the compressor 91.

What is claimed is:

1. A method of absorbing thermal energy at low temperatures comprising alternately compressing a working medium when it is mainly contained in at least one space having a higher mean temperature, and expanding said medium when it is mainly contained in at least one space having a lower mean temperature, passing said medium on its path from one space to another through a heat exchanger thereby delivering thermal energy thereto when flowing to said expansion space and absorbing thermal space, maintaining the pressure of said medium continuously higher than a pressure which is substantially equal to the critical pressure of said medium, and maintaining the temperature at which the expansion takes place in at least one of said spaces below the critical temperature of said medium.

2. A method of absorbing thermal energy at low temperatures as claimed in claim 1 wherein said medium is periodically compressed to above its critical pressure, further supplying said medium while said pressure is maintained substantially constant through a heat exchanger in which said medium delivers thermal energy and is cooled below its critical temperature to an expansion space, thereafter decreasing the pressure of the medium while mechanical energy is withdrawn, said pressure being decreased to a pressure which still is above the critical pressure, and finally discharging said medium from said expansion space while the pressure is maintained substantially constant and again through said heat exchanger where it absorbs energy.

References Cited by the Examiner UNITED STATES PATENTS 1,169,308 1/16 Vuia 62-6 2,567,454 9/51 Taconis 62-6 2,906,101 9/59 McMahon 62-6 2,907,175 10/59 Kohler 62-6 2,966,035 12/60 Gifford 62-6 3,045,436 7/62 Gifiord 62-6 3,091,092 5/63 Dros 62-6 3,101,596 8/63 Rinia 62-6 WILLIAM J. WYE, Primary Examiner.

energy therefrom when flowing from said expansion ROBERT OIEARY Examiner- 

1. A METHOD OF ABSORBING THERMAL ENERGY AT LOW TEMPERATURES COMPRISING ALTERNATELY COMPRESSING A WORKING MEDIUM WHEN IT IS MAINLY CONTAINED IN AT LEAST ONE SPACE HAVING A HIGHER MEAN TEMPERATURE, AND EXPANDING SAID MEDIUM WHEN IT IS MAINLY CONTAINED IN AT LEAST ONE SPACE HAVING A LOWER MEANS TEMPERATURE, PASSING SAID MEDIUM ON ITS PATH FROM ONE SPACE TO ANOTHER THROUGH A HEAT EXCHANGER THEREBY DELIVERING THERMAL ENERGY THERETO WHEN FLOWING TO SAID EXPANSION SPACE AND ABSORBING THERMAL ENERGY THEREFROM WHEN FLOWING FROM SAID EXPANSION SPACE, MAINTAINING THE PRESSURE OF SAID MEDIUM CONTINUOUSLY HIGHER THAN A PRESSURE WHICH IS SUBSTANTIALLY EQUAL TO THE CRITICAL PRESSUR OF SAID MEDIUM, AND MAINTAINING THE TEMPERATURE AT WHICH THE EXPANSION TAKES PLACE IN AT LEAST ONE OF SAID SPACES BELOW THE CRITICAL TEMPERATURE OF SAID MEDIUM. 